1. Field of the Invention
The invention relates to a motor control device for driving a three-phase brushless motor. The three-phase brushless motor is, for example, used as a source for generating steering assist force in an electric power steering.
2. Description of Related Art
A driving circuit of a brushless motor used in an electric power steering is formed to include switching elements, such as field effect transistors (FETs). When a fault occurs in any one of the switching elements, there is a possibility that the brushless motor becomes a load when a steering wheel is operated and, as a result, steering operation becomes heavy. In order to take measures against such a problem, a relay is inserted in a connection between the brushless motor and the driving circuit. Far example, in the case of a three-phase brushless motor, relays are respectively inserted in the motor connections of two phases, and then those relays are turned off during non-control or when a fault occurs in any one of the switching elements.